Electric control system



March 18, 1941. e. w. GARMAN 2,235,551

ELECTRIC CONTROL SYSTE I Original Filed Nov. 24. 193? Fig.1.

Inventor: George W. Garman by M17 6 X H is Attorney.

Patented Mar. 18, 1941 UNITED STATES 2,235,551 ELECTRIC CONTROL SYSTEMGeorge W. Garman,

Scotia, N. Y., minor to General Electric Company, a corporation of NewYork Original application November 24, 1937, Serial No. 176,281. Dividedand this application July 15, 1938, Serial No. 219,381

5 Claims. (Cl. 171-11?) My invention relates to electric control systemsand more particularly to electric valve control systems fordynamo-electric machines.

This application is a division of my copending application Serial No.176,281 filed November 24, 1937 and assigned to the assignee of thepresent application.

In many industrial operations or processes it is frequently desirable tocontrol an operation by means of an electric motor, the speed of whichis precisely and accurately determinable. For example, in manyapplications it is desirable to energize a direct current motor from anassociated alternating current circuit through electric valve means andto maintain the speed of the motor at a definite predetermined speed.Heretofore many of the prior art arrangements which employed for thispurpose have. entailed the use of complicated and expensive controlequipment and have been susceptible to objectionable variations inspeed. Furthermore, it has becomedesirable to provide control apparatuswhich isentirely electrical in nature and operatiorii and which is freeof moving or vibrating contacts. In addition, it is important ingorderto obtain pre cise control to dispense with the use of mechani cal speedresponsive devices because of the inherent limitations of such;arrangements.

It is an object of my invention to provide a new and improved electriccontrol system.

It is another object of my invention to provide a new and improvedelectric valve control system for dynamo-electric machines.

It is a further object of my invention to provide a new and improvedcontrol system for electric valve insulating apparatus for energizing adirect current motor from an alternating current supply circuit.

In accordance with one of the illustrated embodiments of my invention, Iprovide an improved control circuit for controlling an operatingcharacteristic, such as the speed, of a direct current motor. A directcurrent motor is energized from an alternating current supply circuitthrough electric valve translating apparatus including electric valveshaving control members for controlling the conductivities thereof. Anauxiliary dynamo-electric machine or a pilot generator is directlyconnected to the direct current motor to provide a unidirectionalvoltage which varies in accordance with the speed of the motor. Theoutput voltage of the pilot generator acts in opposition to a source ofreference potential, and the resultant or different voltage isintroduced in the excitation circuit for the control members of the havebeen electric valves to control the conductivities of the electricvalvesin accordance with the speed of the motor, thereby controlling thevoltage impressed on the armature of the direct current motor. Aserially connected capacitance and re sist'ance are connected in seriesrelation with the source of reference potential and the armature of thepilot generator to delay the rate of change of the resultant voltageimpressed on the control members of the electric valves, and hence serveas a damping means when the direct current motor speed undergoes suddenvariations. The phase of the voltage impressed on the control members ofthe electric valve means is controlled by means of a phase shiftingcircuit of the static impedance type. The phase shifting circuitincludes a variable impedance, such as an inductance of the saturabletype, having a control winding which is energized in accordance with thedifierence between a source of reference poten tial and theunidirectional voltage produced by the pilot generator. An anti-huntingmeans is connected in circuit with the source of reference potential andthe pilot generator to control the rate of change of the currenttransmitted to the control winding of the variable impedance element.

For a, better understanding of my invention reference may be had to thefollowing description taken in connection with the accompanying drawing,and its scope will be pointed out in the appended claims. Figs. 1 and 2diagrammatically illustrate embodiments of my invention as applied to asystem for controlling the speed of a motor of the direct current type.

Referring now to Fig. 1 of the drawing, my invention is diagrammaticallyillustrated as applied to an electric valve control system for adynamo-electric machine i of the direct current type having an armature2 and a field winding 3. The field winding 3 may be energized from anysuitable source of direct current 4. Armature 2 of machine I isenergized from an alternating current circuit 5 through a transformer Gand through electric valves 1 and 8. The transformer 6 comprises aprimary winding 9 and a secondary winding l provided with electricallyintermediate connections I I, I2 and i3. The electric valves 1 and 8 arepreferably of the type employing an ionizable medium such as a gas or avapor and each comprises an anode I4, a cathode I and a control means ormember 18. One terminal of the direct current armature 2 of machine I isconnected to the intermediate connection ll of secondary winding l0, andthe other terminal thereof is connected to the common connection ofcathodes l5 of electric valves I and 8.

To impress on control members l8 of electric valves 1 and 8alternating-voltages of predetermined phase displaced relative to therespective anode voltages, I employ an excitation circuit including atransformer l'l which may be energized from secondary winding ill oftransformer 8 through a suitable phase shifting circuit l8. Thetransformer I1 is provided with a primary winding [9 and a secondarywinding 20. Current limiting resistances 2| and 22 are connected inseries relation with control members 16 of electric valve means I and 8,respectively. Capacitances 23 and 24 may be connected across thecathodes i5 and control members ii of electric valves 7 and 8,respectively to absorb extraneous transient voltages. A smoothingreactance 25 may be connected in series relation with the armature 2 ofthe motor I.

In order to control the conductivities of the electric valves 1 and 8 inaccordance with an operatingcondition or anelectrical characteristic ofthe directcurrent motor I, the phase shifting circuit 18 is arranged toimpress on the control members l6 of electric valves 1 and 8 a periodicvoltage or an alternating voltage variable in phase with respect to theanode-cathode voltages of these electric valves. The phase shiftingcircuit IB may be of the static impedance phase shifting type and mayinclude a serially connected resistance 26 and a variable impedancemember, such as aninductance 21 which may be of the saturable type. Theserially connected resistance 26 and the inductance 2'! may be connectedto terminals or taps I 2 and i3 of winding iii. The variable inductanceelement 21 is provided with a control winding 28 which is energized in amanner described hereinafter.

As an agency for controlling the phase of the resultant voltagesimpressed on the control members iii of electric valves 1 and 8 inaccordance with a predetermined controlling influence derived from thedynamo-electric machine I, I employ a voltage source variablein'accordance with the condition to be controlled. The voltage sourcemay comprise an auxiliary dynamo-electricmachine 29 which may be termeda pilot generator. The pilot generator 29 may be of the direct currenttype having an armature member 30 and a field winding 3! which may beenergized from any suitable source of direct current and which is shownas being connected to the direct current circuit 4.

A voltage divider 32 including a resistance 33 may be connected inseries relation with the direct current circuit 4 and the field winding3 of the direct current motor I and serves as a means for controllingthe energization of the field windmg. The voltage divider 32 may beprovided with an adjustable contact 34.

I provide a voltage divider 35, comprising a resistance 36 and anadjustable contact 31, for producing a variable or an adjustable sourceof reference potential against which the output voltage of the pilotgenerator 29 acts. The voltage divider may be energized from anysuitable source of unidirectional voltage 38. It will be noted that thevoltage of the voltage divider 35 and the voltage of the pilot generator29 act in opposition to control the resultant current transmittedto thecontrol winding 28 of the variable inductance element 21 of the phaseshifting circuit i8.

As an agency for controlling the energization capacitance 38 and aresistance 40. A unidirectional conducting device M is connected inseries relation with the control winding 28. The capacitance 33,resistance and armature 30 of the pilot generator 28 are connected inseriesrelation across armature 2 of motor I. The voltage appearingacross the terminals of the resistance 40 is in a direction tending tooppose that introduced into the circuit by the pilot generator 29 andoccasioned by variations in the speed of the direct current motor I. Thevoltage divider 35 is adjusted so that the voltage supplied thereby isgreater than that produced by the pilot generator 23.

The operation of the embodiment of my invention shown in Fig. 1 will beexplained by considering the system when dynamo-electric machine l isoperating as a direct current motor and when the armature 2 thereof isvariably energized from the alternating current circuit 5. A variableunidirectional current is transmitted to the armature 2 of motor Ithrough electric valves "I and 8 which operate as-a controlledrectifier. p

The manner in which the electricvalves I and 8 control the voltageimpressed on the armature 2 of the motor I will be well understood. bythose skilled in the art. For a given positive anode voltage there is acertain value of grid voltage which I is termed the control gridvoltage. When the grid voltage is more negative than this value, currentcannot flow between anode and cathode. If the grid voltage is morepositive than this critical value, current can flow and the magnitude'ofthe current will be determined by the extent of resistance of theassociated circuit. Once this circult is established between anode andcathode in the usual commercial arrangement, the grid can exert nofurther control unless the anode voltage is reduced to a value nearzero. When the anode voltage becomes zero, the current flow ceases andif the grid is sufficiently negative it can then prevent the currentfrom re-starting. Therefore, when the voltage is applied between thecathode and anode, the grid can regain con= trol once during each cycleand can, therefore, be used to prevent current flow when the anode ispositive.

The impedance phase, shifting circuit l8 impresses on the controlmembers or grids N5 of electric valves I and 8 alternating voltagesvariable in phase to control the conductivities thereof in accordancewith the speed of the mo-v portion of resistance 38 of the voltagedivider 35, resistance 40, the unidirectional conducting device 4| andarmature 30 of pilot generator 29.

It will be noted that the voltage produced by the pilot generator 29 isin opposition to that produced by the voltage divider 88.

For example, if it be assumed that the speed of the direct current motorI decreases to a value below the predetermined value to be maintained,the voltage produced by the pilot generator 29 will decrease, efi'ectingthereby an increase in the resultant unidirectional voltage acting inthe circuit which energizes the control winding 28 01 the saturabiereactance 21. As a result thereof, the current supplied to the controlwinding 28 is increased, effecting an advance in phase of thealternating voltages impressed on the control members I6 of electricvalves "I and 8, and causing the electric valves to impress on armaturemember 2 of the direct current motor I an increased unidirectionalvoltage tending to restore the motor speed to the predetermined value.The antihunting circuit including the capacitance 39 and resistance 49will respond to introduce in the circuit a compensatory efiect tendingto prevent the overshooting of the controlling action. For

example, when the electric valves I and 8 increase the voltage appliedto the armature member 2, the lower terminal of the armature 2 will beraised to a value more,positive than the previously prevailing value anda current will flow through the capacitance 39, armature 39 of pilotgenerator 29 and resistance 49. This current will be in a direction suchthat the lower terminal of the resistance 49 will be at a potentialpositive relative to the upper terminal. The voltage of the resistance49 is in a direction tending to oppose that occasioned by the change inspeed of the motor I. In other words, the voltage across the resistance40 tends to decrease the increment of current transmitted to the controlwinding 28 under the conditions above described. In this manner ananti-hunting action is introduced to prevent overshooting "of thecontrolling action. The unidirectional conducting device 4| insures thatonly unidirectional current is supplied to the control winding 28. Ofcourse, the system responds to decrease the speed of motor I, when itsspeed increases above the desired value. v

Fig. 2 illustrates another embodiment of my invention as applied to anelectric valve system for variably energizing the excitation or fieldcircuit of the direct current motor I to control the speed thereof. Thearrangement of Fig. 2 is similar in many respects to that oi Fig. 1, andcorresponding elements have been assigned like reference numerals. Theelectric valves 1 and 8 variably energize the excitation circuit 3 ofmotor I to control the speed thereof. The voltage divider 35 is adjustedso that the voltage produced thereby is less than the output voltage ofthe pilot generator 29.

I provide a serially connected unidirectional conducting device 42, aresistance 43 and a capacitance 44 which are connected to be responsiveto the voltage of the excitation or field winding 3 of the motor I. Theunidirectional conducting device 42, resistance 43 and capacitance 44may be connected in series relation with a resistance 45 so that thecomplete circuit is connected across the field or excitation winding ofmachine I. In this arrangement contact 3'! is adjusted so that thevoltage supplied by voltage divider 35 is less than that produced bypilot generator 29. A parallel connected capacitance 48 and resistance41 are connected between the lower terminal of resistance 45 and thepositive terminal of the direct current motor I to introduce into thecontrol circuit a voltage which 3 varies in accordance with the rate ofchange of the voltage applied to the terminals of field winding 8. i v

The embodiment 01' my invention shown in Fig. 2 operates insubstantially the same manner as that explained above in connection withFig. l. The field winding 3 01 the direct current motor I is variablyenergized from the alternating current circuit 5 through electric valvesI and 8 in accordance with the speed of the direct current motor I. Thealternating voltages impressed on control members I8 are varied in phaseto control the conductivities of the electric valves I and 8. Controlwinding 28 of the saturable inductive reactance 21 is variably energizedin accordance with the difierence in voltages produced by the pilotgenerator 29 and the voltage divider 35. The control winding 28 isenergized through a circuit including armature 39 of pilot generator 29,the unidirectional conducting device 42, resistance 43 and the upperportion of the resistance 38 of the voltage divider 35.

For example, if it be assumed that the speed of the direct current motorI increases to a value above the predetermined value to be maintained,the resultant unidirectional voltage impressed on the control winding 28is increased due to the increase in voltage of the pilot generator 29.Coincidentally therewith, the unidirectional current supplied to thecontrol winding 28 is increased to effect an advancement in phase of thealternating voltages impressed on the control members I6 of the electricvalves I and 8 relative to the applied anode-cathode voltages, so thatthese valves increase the average current transmitted to field winding 3of direct current motor I, thereby tending to reduce the speed to thepredetermined value. The circuit including the unidirectional conductingdevice 42,!esistance 43, capacitance 44 and the resistance 45 functionsto introduce an anti-hunting efiect into the circuit for control winding28 in the following manner. Under the conditions stated, when theelectric valves I and 8 increase the voltage applied to the fieldwinding 3 of motor I, a charging current will flow through the circuitincluding the unidirectional conducting device 42, resistance 43,capacitance 44 and resistance 45. The charging current is in a directionwhich tends to maintain the left-hand terminal oi! resistance 43negative relative to the right-hand terminal, and this voltage is in adirection opposite to the increase in voltage of the pilot generator 29occasioned by the increase in speed. In this manner, the regulatoryaction of the voltage of the pilot generator 29 is partiallycompensated, tending to prevent overshooting of the regulatory action.The capacitance 46 and resistance 45, which are also connected acrossthe field winding 3 of machine I, tend to stabilize the action of theregulating system by introducing in the circuit for these elements avoltage which tends to limit the anti-hunting action. 0: course, thesystem responds to raise the speed of motor I when the speed decreasesbelow the desired value.

While I have shown and described my invention as applied to particularsystems of connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention,

1 and I, therefore, aim in the appended claims to What I claim as newand desire to secure-by Letters Patent 01' the United States, is:

LIn combination, an ternating currentsupply circuit, a dynamo-e ectricmachine having excitation and armature circuits, electric translatingapparatus for energizing at least one of said circuits from saidalternating current circuit and comprising an electric valve meanshavinga control member, an impedance phase shifting circuit comprisingan inductive saturable reactance for impressing on said control member aperiodic voltage variable in phase relative to the voltage of saidalternating current circuit to control the cdnductivity of said electricvalve means, said saturable reactance having a control winding, a pilotgenerator for producing a unidirectional voltage which varies inmagnitude in accordance with a predetermined controlling infiuencederived from said first mentioned machine for variably energizing saidcontrol winding,

means for producing a substantially constant uni directional referencevoltage which is greater inlating apparatus for energizing at least oneof said circuits from said alternating current circult and comprising anelectric valve means having a control member, an impedance phaseshifting circuit comprising an inductive saturable reactance forimpressing on said control member a periodic voltage variable in phaserelative to the voltage of said alternating current circuit to controlthe conductivity of said electric valve means,

said saturable reactance having a control winding, a pilot generator forproducing a voltage which varies in accordance with a predeterminedcontrolling influence derived from said first mentioned machine forvariably energizing said control winding, a source of direct current anda voltage divider for producing a substantially constant unidirectionalreference voltage greater in magnitude than the voltage of said pilotgenerator, anti-hunting means comprising a serially connected resistanceand a capacitance connected to be responsive to a resultant of thevoltage of either of said circuits of said machine and the voltage ofsaid pilot generator for modifying the regulatory action of saidperiodic voltage, and a unidirectional conducting device connected incircuit with said anti-hunting means and said control winding to assurethat only unidirectional current is transmitted to said control windingduring voltage variations of said pilot generator thereby limiting therange of phase shift of said periodic voltage.

3. In combination, an alternating current circuit, a dynamo-electricmachine having excitation and armature circuits, electric translatingapparatus energized from said alternating current circuit for energizingsaid armature circuit and comprising electric valve means having acontrol member, an impedance .phase shifting circuit for impressing onsaid control member a aeeaaci periodic voltage variable in phaserelative to the voltage of said alternating current circuit to controlthe conductivity of said electric valve means and comprising a saturableinductive reactance having a control winding, a source of unidirectionalvoltage, a voltage divider connected to said source to produce asubstantially constant unidirectional reference voltage, a pilotgenerator for roducing a voltage which is smaller in magnitude than saidreference voltage and opposes said unidirectional reference voltage andwhich varies in J accordance with a predetermined controlling influencederived from said first mentioned machine with said armature circuit,sai'd voltage divider I and said control winding to modify theenergization of said control winding in accordance with the rate ofchange of the voltage of said armature circuit, and a unidirectionalconducting de- '-'vice connected in circuit with said anti-hunting meansand said control winding to assure that only unidirectional current istransmitted to said control winding during voltage variations of saidpilot generator.

4. In combination, an alternating current circuit, a dynamo-electricmachine having excitation and armature circuits, electric translatingapparatus energized from said alternating current circuit for energizingsaid armature circuit and comprising electric valve means having acontrol member, an impedance phase shifting cir-'- cuit for impressingon said control member a periodic voltage variable in phase relative tothe .voltage of said alternating current circuit to control theconductivity of said electric valve means and comprising a saturableinductive reactance having a control winding, a source of unidirectionaivoltage, a voltage divider connected across said source to provide asubstantially constant unidirectional reference voltage, a pilotgenerator for producing a voltage which is of smaller magnitude thansaid reference voltage and opposes said unidirectional voltage and whichvaries in accordance with a predetermined controlling influence derivedfrom said first mentioned machine for variably energizing said controlwinding, anti-hunting means comprising a serially connected resistanceand a capacitance connected in circuit with ,the armature circuit, saidvoltage divider and said control winding to control the energization ofsaid control winding in accordance with the rate of change of thevoltage of said armature winding, and a unidirectional conducting deviceconnected in series relation with said control winding and said armaturecircuit to assure that only unidirectional current is supplied to saidcontrol winding during voltage variations of said pilot generator.

5. In combination, an alternating current supply circuit, adynamo-electric machine having excitation and armature circuits,electric translating apparatus energized from said alternating currentcircuit for energizing said excitation circuit and comprising anelectric valve means having a control member, an impedance phaseshifting circuit for impressing on said control member 'ducing asubstantially constant reference voltage,

a pilot generator for producing a voltage which is smaller in magnitudethan said reference voltage and which varies in accordance with apredetermined controlling influence derived from said first mentionedmachine for variably energizing said control-winding, and anti-huntingmeans connected across said excitation circuit and comprising a seriallyconnected unidirectional conducting device, a capacitance and aresistance for modifying the effect of the voltage of said pilotgenerator in accordance with the rate of change of the voltage appliedto said excitation circuit, said unidirectional conducting deviceserving to assure that only unidirectional current is transmitted tosaid control winding during voltage variations of said pilot generator.

GEORGE W. GARMAN.

